RF board Beacon transmitter RF board bottom

Recovery system

The recovery system is based on three main parts, the GPS, Beacon transmitter and Satellite modem. These components are all mounted on the RF board in the eBox which also is populated with the antenna connectors. The GPS is the first part in the recovery system chain. It is a standard of the shelf chip (GlobalSat ET318). It is connected to the FPGA which then forwards the signals to the transmitters in two different formats. The first format is the GGA standard GPS message string which is produced directly by the GPS module. This message is buffered by the FPGA so that it later can be forwarded to the beacon in a lower sample rate. The second format is custom made and only contains a hex string with the coordinates. The idea is to minimize the data size of each string. The string is further forwarded to the satellite modem.

Beacon transmitter

The beacon transmitter is based on a Radiometrix TX1 10 mW transmitter which transmits on 173.225 MHz. During descent and once every 15 minutes the system forwards the GGA messages from the GPS receiver and transmits it using frequency modulation at 2400 BAUD.

The transmitter is enabled at about T+250s by its own activation circuit however it is drastically dampened until parachute deployment due to the metal top cover off the FFU. Even though the beacon is not currently the GGA message it is continuously transmitting the carrier wave at 173.225 MHz. It is fully possible to track the FFU based on just the carrier wave and a tracking receiver.

Satellite modem

The satellite modem is a AeroAstro STX2 modem which transmits at 1.615 GHz. The idea is that the satellite modem transmits the GPS coordinated given by the GPS and formatted by the FPGA. The messages are received by the GloalStar satellite network, which forwards it to AeroAstro servers where it is stored and can later be accessed by a web user interface. The modem is activated during the descent and remains on for the first 30 minutes. It is then switched of to save power but is turned on again for two minutes each fifteen minutes.